1. Technical Field
The present invention generally relates to esterified copolymers of polyalkenes and unsaturated acidic reagents (“UAR”) and their use as lubricant and fuel additives. More particularly, the present invention is directed to reaction products derived from polyols and copolymers of polyalkenes, e.g., polyisobutenes (“PIB”), and unsaturated acidic reagents, a process for making same and the use of the reaction product as (1) a friction modifier for lubricating oils such as automatic transmission fluids to improve torque capacity, viscosity control and anti-shudder durability and for continuously variable transmissions (CVTs), (2) a friction modifier for fuels and (3) a cold flow improver for diesel fuels. The esterified polyalkene/UAR copolymer reaction products may be used as is or can be further derivatized (e.g., by post treatment of the reaction product with, for example, boric acid).
2. Description of Related Art
Esterified polyisobutenyl succinic anhydrides have been used as additives for lubricating oils, e.g., commercially available succinate pentaerythritol esters such as Lubrizol 936 available from The Lubrizol Corporation (Wickliffe, Ohio). These esters have been generally prepared by reacting polybutylene and maleic anhydride under suitable conditions to form a polybutene/maleic anhydride monomer (PIBSA) and then further reacting the monomer with pentaerythritol to provide an esterified polybutene/maleic anhydride monomer.
In addition, copolymers of polyisobutene and maleic anhydride have also been prepared. These copolymers are sometimes referred to as “polyPIBSA”. They can be prepared by copolymerizing a polybutene containing a high concentration of the methylvinylidene isomer (along with other polybutene isomers) with an unsaturated acidic reagent such as maleic anhydride using a free radical initiator. See, e.g., U.S. Pat. Nos. 5,112,507 and 5,616,668.
U.S. Pat. No. 6,451,920 discloses a process for preparing a polyPIBSA/acid-catalyzed thermal PIBSA monomer mixture employing the steps of (a) copolymerizing (1) polybutene containing alkylvinylidene isomer and non-alkylvinylidene isomers and (2) an unsaturated acidic reagent under polymerization conditions in the presence of a free radical initiator; and (b) reacting the product of step (a) with an unsaturated acidic reagent at elevated temperature in the presence of a strong acid. These polyPIBSA/acid-catalyzed thermal PIBSA monomer mixtures contain a high ratio of anhydride units per polybutene unit as evidenced by a succinic ratio greater than one (as shown in the '920 patent examples). This high succinic ratio is related to multiple anhydride units per polybutene within the thermal PIBSA monomer, and to the presence of poly-anhydride resin. The mixture can be further reacted with an amine to form a polysuccinimide or with a polyol to form a polyester. When reacting the polyPIBSA/acid-catalyzed thermal PIBSA monomer mixture with a polyol, crosslinking between the polyPIBSA, acid-catalyzed thermal PIBSA and resin results.